Royal Mail bosses are under pressure to avert a Christmas meltdown after photos appeared to reveal a huge backlog of items from a wave of strikes.
Images said to have been taken in the last few days show mountains of packed mail bags and cages piling up at depots in North West England, South West London and Essex.
The latest 48-hour strike by members of the Communication Workers Union ends on Thursday, at the start of the busy festive period.
But more stoppages are planned up to Christmas Eve unless there is a breakthrough in the row over issues including pay, redundancies and start times.
The CWU claims Royal Mail wants to become a parcel courier reliant on casual labour.
The union has accused boss Simon Thompson of refusing to attend what it claimed was a key meeting last week.
General secretary Dave Ward said: “It’s beyond me why he didn’t bother turning up to the meeting that could have averted these strikes.
"Simon Thompson’s obsession with forcing through the destruction of workers’ living standards has risked a national mail meltdown at Christmas.”
He said of the backlog: “Posties are willing to bend over backwards to clear it and get Christmas back on track.”
More strikes are scheduled for December 9 and 11, with 48-hour stoppages on December 14 to 15 and 23 to 24. Royal Mail said it will deliver as much priority mail as possible on strike days.
It said Mr Thompson has been involved in the talks with the CWU for seven months, including four weeks of talks at conciliation service ACAS.
He was not at the meeting last week but a source claimed it was held online and lasted a few minutes.
Royal Mail added: “We have the best pay and conditions in our industry. In an industry dominated by insecure work and low pay, our model sets us apart and we want to preserve it. We remain available to meet to discuss our best and final offer worth up to 9%.”